This invention relates to methods of detecting asbestos and more particularly to the preparation of asbestos samples for use in x-ray optics for measuring the asbestos within an air sample.
Heretofore analysis of elements, samples of materials, crystals, etc., have been carried out by x-ray optics since it is well known that they have a characteristic x-ray pattern. Most fibers other than asbestos are single crystals with a major axis along the fiber direction. Preferred orientation is observed for planes normal to the fiber axis but not for planes parallel to the axis. Thus the measurement of asbestos fibers are very difficult especially in a mixed sample.
One factor which makes measurement of asbestos difficult is the quantity which can be collected from a reasonable amount of air is far too small to measure with x-ray film cameras. Therefore diffractometers with electronic detectors are required, however other problems are introduced because of the peculiar morphology of crystalline matter. Chrysotile asbestos, like all crystals, has a characteristic x-ray diffraction pattern. However, platy serpentines has almost exactly the same x-ray pattern as chrysotile and many other clay minerals have very similar patterns. It has been determined that the morphology of chrysotile asbestos is like that of a "rolled up" sheet of crystalline matter with the a-axis parallel to the fiber axis, the c-axis is nearly perpendicular to the "tubular" wall, with the b-axis perpendicular to a and c axis. Thus, the axes (b and c) take different orientations depending on where on the fiber they are set up. Preferred orientation can be observed from the planes parallel to the fiber axis using the well known x-ray diffraction camera technique, however such methods cannot be adapted to airborn asbestos samples since it is not possible to form the fibers in the required small bundles. Further, it has been determined that even with an oriented sample the major crystal plane (002) diffracts equally well for either orientation. Therefore well known x-ray optics cannot be used for detecting asbestos in samples. A suitable system has been set forth in a publication NRL Report 7874, Quantitative Analysis of Airborn Asbestos by X-Ray Diffraction, by L.S. Birks and M. Fatemi, J.V. Gilfrich and E.T. Johnson, Naval Research Laboratory, Washington, D.C. 20375, which forms a part of this specification. U.S. Pat. No. 3,497,419 is directed to electrostatic alignment of asbestos fibers. This approach to alignment of asbestos fibers is not directly applicable to the present invention because the patent is concerned with long, silky industrial fibers and with large quantities of material. This invention is concerned with measurement of aerosol and other small samples to determine the presence and quantity of small asbestos elements in the sample.